I would like to provide (in some cases) an initial question template which is shown in the editor (instead of an empty text area) when a user asks a question. Preferrably, I'd like to provide this text via the URL, something like:

This works, thanks! And it actually works even better than @Ami's version (there, some characters have not been transmitted correctly, for example ">" was displayed as "&gt;" (or so - I mean the html code)). This way is better with regard to upgrades, too - but what happens if the editor plugin is upgraded?

You'll have to apply this patch again. Anyway, you can't get away without doing so because, as I mentioned above, it is the editor plugin itself what you want to change. If you want to have a longer term solution, you could probably clone the plugin apply this patch and use that custom plugin instead of the default one. But again, it is your call... of course, the safest thing to do will always be not to change anything and use the code core/plugin code as it is :)

Thank you, sounds good, but it didn't work so far... First, I don't have a *qa-include/pages* folder. I used *qa-include/qa-page-ask.php* - is that right? It looks very similar. But when I insert your code, the page just stays white, no content at all. (I have no experience with PHP.)

One extra thing I just realised, I think you will need to put qa_html() around the content, because otherwise someone could put something bad in the URL (like a bad javascript) and it will end up on the page.

$in['content'] = qa_html(qa_get('template'));

Also, this is not really the best way to do things because your changes will be lost when upgrading Q2A. You should look into making a plugin to do that.